An arrangement was proposed in U.S. Pat. Nos. 3,596,379 and 3,707,786 of planet projection units in a carrier frame in several planes one above the other under the main instrument. This carrier frame can be moved together with the projectors both around the longitudinal axis of the system and also about a horizontal axis. To prevent the individual planet projectors screening each other off, the carrier frame is arranged at a given angle to the longitudinal axis of the system. Such an arrangement of the planetary projection units does in fact avoid the problem of screening by the main instrument; however, enormous mechanical problems arise. Balancing weights are necessary for the tilted carrier frame for the required longitudinal axis rotational motion, and likewise for rotation of the carrier frame together with the projection units about the horizontal axis. These balancing weights are required in order to compensate for the respective asymmetric weight distribution about the axis of rotation. Problems arise with the precision drives which are necessary for such systems. Restrictions thus arise both on space and on weight in the choice of the planet projection units. A further disadvantage is that the required signal and supply leads to the projection units have to be passed through at least two expensive slip ring systems. In addition to this, the control of the two rotational motions is very expensive.